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  <title>Document</title>
  <style>
    div {
      border: 1px solid #000;
      /* w20+h30+m40+p50 */
      width: 20px;
      height: 30px;
      margin: 40px;
      padding: 50px;
    }
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</head>
<body>
  
  <div class="box"></div>
  <div id="main"></div>

  <!-- 根据场景自动判断 -->
  <!-- ul>.item{列表元素$}*5 -->
  <ul>
    <li class="item">列表元素1</li>
    <li class="item">列表元素2</li>
    <li class="item">列表元素3</li>
    <li class="item">列表元素4</li>
    <li class="item">列表元素5</li>
  </ul>

</body>
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